With reference to document FR 2 790 583 (SAMSUNG), especially to FIG. 4 of that document reproduced schematically hereinbelow in FIG. 1, the invention relates to a method for driving an AC image-display plasma panel with coplanar sustain discharges, and with memory effect, of the type comprising:                a front tile and a rear tile, which are parallel and provide between them a space filled with a discharge gas;        one 12 of the tiles comprising at least a first array of electrodes 5 and the other tile 11 comprising at least a second array of triads of electrodes 13, 20, 14, the general direction of which is approximately orthogonal to that of the electrodes 5 of the first array;        the spaces located at the intersections of the electrodes 5 of the first array with the triads of electrodes 13, 20, 14 of the second electrode array forming a matrix of light-discharge regions 9 and of dots of the image to be displayed;        the electrodes 13, 20, 14 of the triads being coated with a dielectric layer 17 in order to obtain the conventional memory effect whereby a discharge may be generated between these electrodes by applying a voltage below the ignition voltage.        
In general, the walls of adjacent discharge regions are partially fitted with phosphors emitting different colours when they are excited by the ultraviolet radiation from the discharges; thus, the adjacent dots corresponding to these regions of different colours are combined into pixels or picture elements of the image to be displayed.
In general, the discharge regions, at least those of different colours, are separated by barriers.
The abovementioned memory effect is obtained in a discharge region 9 once charges are deposited on the surface of the dielectric 17 in this region, especially by applying a pulse called the address pulse between the electrode 5 and at least one of the opposed electrodes of the triad 14, 20, 13 which intersect in this region; the dielectric layer is generally coated with a protective layer which also emits secondary electrons, for example an MgO-based layer.
To obtain a succession of sustain discharges in the regions thus “addressed”, the driving method described in that document comprises:                conventionally, the application of at least one series of sustain voltage pulses between the opposed electrodes 13, 14 of each triad so as to generate sustain discharges in each of the “addressed” intersection regions 9, that is to say that in which it is desired to sustain a discharge;        furthermore, at a time prior to (claim 3) or at the same time (claim 6) as the time when a sustain pulse of this series was applied, application of a pulse to the central electrode 20 of the said triad so as:        either (claim 4) to raise the potential of the central electrode 20 to the level of the higher potential [central=anode] of the two opposed electrodes 13, 14 at the moment of the said sustain pulse generating a sustain light discharge and then, when the said discharge decreases, to lower the potential of this central electrode 20 to the level of the lower potential of the two opposed electrodes 13, 14 [central=cathode],        or (claim 5) to lower the potential of the central electrode 20 to the level of the lower potential [central=cathode] of the two opposed electrodes 13, 14 at the moment of the said sustain pulse generating a sustain light discharge and then, when the said discharge decreases, to raise the potential of this central electrode 20 to the level of the higher potential of the two opposed electrodes 13, 14 [central=anode].        
The timing diagrams corresponding to the staggering of the pulses and of the discharges are shown, on the one hand, in FIGS. 5 and 6 and, on the other hand, in FIGS. 8 and 9 of that document.
Again according to that document FR 2 790 583, the central electrode 20 must be thin so as not increase the electrostatic capacitance of the sustain electrodes of each triad.
In coplanar sustain-discharge plasma panels, the discharges occur by charge transfer across the region 9 onto the inner surface of the dielectric layer 17 of the tile 11 bearing the coplanar electrodes, in this case the triads 13, 20, 14; a description will now be given of the various charge transfer steps which optionally give rise to sustain light discharges in the case of the driving of a panel like the one described in document FR 2 790 583 and reference will be made to the appended FIGS. 2A to 2H1 in which the regions filled with “−” symbols represent negative charges or electrons on the surface of the dielectric 17 and in which the chequered regions correspond to positive charges or ions on the surface of the dielectric 17:                after a conventional address pulse applied to an intersection of an electrode 5 of the first array with a triad of electrodes 13, 20, 14 of the second electrode array, between this address electrode 5 and at least one electrode of this triad, the charge distribution illustrated in FIG. 2A is obtained, the electrode 14 being raised to +300 V with respect to the other electrodes 20 (0 V) and 13 (0 V); electrons therefore accumulate on a lateral electrode of the triad and ions accumulate mainly on the central electrode of the triad;        as in a conventional sustain sequence, the potentials of the two lateral electrodes are reversed and the electrode 13 is raised to +200 V with respect to the opposed lateral electrode 14 (0 V); at the moment of application of this first sustain pulse, the potential of the central electrode 20 is then raised to the level of the higher potential of the two opposed electrodes 13, 14, i.e. in this case 200 V, and the central electrode then acts as anode; this results in the configuration illustrated in FIG. 2B1 and a first main sustain light discharge occurs (see arrow) which causes the charge reversal shown in FIG. 2C1; during this charge reversal, the electrons spread out over the width of the central electrode 20 and over that of the lateral electrode 13, thereby giving rise to a substantial extension of the positive pseudocolumn of the plasma and therefore to a discharge of high luminous efficiency;        then, when this discharge decreases, the potential of the central electrode 20 is lowered to the level of the lower potential of the two opposed electrodes 13, 14 (in this case 0 V), and the central electrode then acts as cathode, as shown in FIG. 2B2; the movement (arrows) of the charges which is then initiated generates a first secondary sustain light discharge and results in the charge distribution shown in FIG. 2C2; this discharge has a poor luminous efficiency as it does not give rise to significant and extensive spreading of the electrons;        
the second sustain pulse is now applied, by again reversing the potentials of the two lateral electrodes; the electrode 14 is now raised to +200 V with respect to the opposed lateral electrode 13 (0 V); at the moment of application of this second sustain pulse, the potential of the central electrode 20 is then again raised to the level of the higher potential of the two opposed electrodes 13, 14, i.e. in this case 200 V, and the central electrode then acts as anode; this results in the configuration illustrated in FIG. 2D1; the second main sustain light discharge (see arrow) awaited has barely taken place, as the central region of the surface of the dielectric has been greatly discharged and the memory effect is partly lost; the preceding sequence has therefore resulted in self-erasure; the resulting charge configuration is very little modified (FIG. 2F1);                next, the potential of the central electrode 20 is again lowered to the level of the lower potential of the two opposed electrodes 13, 14, in this case 0 V, and the central electrode then acts as cathode, as shown in FIG. 2D2; the movement (arrows) of the charges which is initiated then generates a second secondary sustain light discharge and results in the charge distribution shown in FIG. 2F2; this discharge has a poor luminous efficiency, as the spreading to which this gives rise relates in this case to ions;        after this first complete sustain cycle comprising two main sustain pulses, a second cycle is then initiated; the first sustain pulse of the second cycle is thus applied by again reversing the potentials of the two lateral electrodes; the electrode 13 is now raised to +200 V with respect to the opposed lateral electrode 14 (0 V); at the moment of application of this sustain pulse, the potential of the central electrode 20 is then again raised to the level of the lower potential of the two opposed electrodes 13, 14, i.e. in this case 200 V, and the central electrode acts as anode; this results in the configuration illustrated in FIG. 2G1 and a new main sustain like discharge occurs (see arrow) which causes the charge reversal shown in FIG. 2H1, identical to FIG. 2C1 showing the end of the first sustain discharge; during this charge reversal, the electrons spread out over the width of the central electrode and over that of the lateral electrode 13, giving rise to an extensive elongation of the positive pseudocolumn of the plasma and therefore to a discharge of high luminous efficiency.        
The second sustain cycle then continues like the first cycle and the movements of the charges are identical to those of the first cycle: from the end of this first main sustain discharge of the second cycle (FIG. 2C1 identical to 2H1), there follow in succession a secondary discharge of low efficiency resulting in self-erasure (FIGS. 2B2 and 2C2), a very low main sustain discharge (FIGS. 2D1 and 2F1) and finally another secondary discharge of low efficiency (FIGS. 2D2 and 2F2).
Where appropriate, further identical sustain cycles then follow in succession until exhaustion of the desired sustain duration, and the voltage pulses applied to the electrodes form a series of sustain pulses.
It may therefore be seen that, over a complete cycle comprising two main sustain pulses and two secondary sustain pulses, only one discharge has a high luminous efficiency; overall, the luminous efficiency of the plasma panel is therefore unsatisfactory when arrays of electrode triads and the driving method described in document FR 2 790 583 are used for coplanar display.
It may therefore be seen that, in a series of sustain pulses, the central electrode acts alternately as anode and cathode.
Moreover, the small width of the central electrode of these triads, like that described and recommended in document FR 2 790 583, limits the possibility of electrons spreading and the possibility of extension of the positive pseudocolumn of the plasma, thereby making no improvement to the luminous efficiency compared with the conventional coplanar configurations, the improvement in luminous efficiency not being, moreover, the objective pursued by that document.
The object of the invention is to provide a coplanar plasma panel structure and a method of driving the sustain pulses for this panel which substantially improve the luminous efficiency; the object of the invention is in particular to avoid the aforementioned drawbacks.